Fiber optic cables are widely used in communications systems. Communications services provided over fiber optic cables are typically either supported by a steel messenger strung between structures (“strand and lash” method), or are of a self-supporting nature using internal strength members. With reference to FIG. 1 there are illustrated aspects of a prior art “strand and lash” installation. Fiber optic cable 10 is supported by a steel messenger 20 strung between support structures 60. The fiber optic cable is physically secured to the steel messenger 20 using a lashing wire 30. This lashing wire is usually made of aluminum or steel. The lashing wire is wrapped around both the fiber optic cable and the messenger, and is usually conductive. FIG. 1 also illustrates splice closures 40 that can be mounted inline, and a short section of repair fiber 50 between the two closures.
All-dielectric, self-supporting (ADSS) fiber optic cable contains no metal or electrically conductive material, and has the capability of supporting its own suspension. Aramid yarns or other non-metallic strength members are arranged so that the tensile load of the cable is applied to the strength members and not the optical fibers. Therefore no separate steel messenger is required. Because the sheath and strength members are integral to the cable's strength carrying ability, the integrated cable must be relieved of tension before the sheath can be cut (which is required to access internal fibers). Devices that are used to connect the cables to supporting structures must grip the cables in a manner such that the tensile load from the cable is properly transferred from the cable strength members through the cable sheath to the supporting apparatus, without damaging the internal optical fibers.
FIG. 2 illustrates an ADSS fiber optic installation, whereby ADSS fiber optic cable 70 is supported by a series of support structures 60, typically utility poles. At each location where access to the fiber is required, the cable is dead-ended (an industry term meaning that the cable tension is transferred to a supporting structure) using a device that is of varying design. For example, FIG. 2 illustrates two such designs: a wedge type deadend 90 and a wire wrap “preform” style 80. The wedge type deadend uses a fixed outer bracket with a sliding wedge that transfers line tension into the wedge, effectively gripping the cable on two sides. One example of a wedge type deadend is that disclosed in U.S. Pat. No. 5,647,046 to Cowen et al. titled “Wedge Deadend to Support Aerial Cables”. The wire wrap preform style is similar to a Chinese finger in that the deadend apparatus “grabs” the entire circumference of the cable once it is wrapped around the cable. One example of such a wire wrap preform style is the Fiberlign product(s) manufactured by PLP (Preformed Line Products) of Cleveland, Ohio. The remaining portion of the cable that is not under tension is routed into a splice closure 100. An example of a splice closure 100 is the Coyote Dome products available from Preformed Line Products of Cleveland, Ohio.
ADSS has inherent benefits over lashed systems. Since the ADSS installation only requires the installation of a single cable, the installation method is faster, and therefore less expensive than the installation of a lashed system. Constructing cable is a 3 step process with a strand and lash system. First, the steel messenger is strung between supporting structures and pulled to tension. Second, the fiber optic cable is placed adjacent to the steel messenger cable. Third, a steel wire is “lashed” around both, holding them together. ADSS construction is simply step one: stringing the cable and pulling to tension. ADSS can also be installed in applications where its dielectric nature is a significant requirement, such as in the supply zone (where power lines are typically installed) of a jointly used pole line. This has made ADSS cable very attractive for power companies and municipalities that have access and qualified personnel to work within the power supply area of the pole. The metal-free, dielectric design also eliminates the bonding and grounding requirements of the traditional steel supported fiber optics installations.
ADSS cable also has drawbacks. Most notably, the cable itself holds the tension required to stay suspended. Consequently, accessing the fiber within the cable currently requires a dead-end assembly that can hold the line tension while giving access to the internal fibers. In contrast, again referring to the traditional strand and lash arrangement of FIG. 1, a cable damaged mid-span is illustrated as repaired by attaching two splice closures 40 and a short section of repair fiber 50 between the two closures. This would usually require breaking all of the fibers within the cable and re-splicing original cable on both ends to repair the cable.
A variety of factors can cause damage to fiber optic cables, including inclement weather, vehicle accidents, tree branches, malicious or inadvertent human-related damage, and animal-related damage (such as squirrels chewing through the sheath of a cable). All of these would result in damaging the fibers therein. Current techniques for repairing mid-span damage to the ADSS cable, however, generally require completely severing and dead-ending the cable at two adjacent structures and placing two splice closures, and the replacement of the entire span of fiber optic cable. FIG. 2 depicts a known ADSS fiber optic installation after the repair of mid-span damage. The ADSS fiber optic cable 70 is dead-ended at the structures adjacent to the damage. A repair section 110 is then constructed between the structures. The original cable 70 is spliced to the repair fiber 110 using traditional closures 100, which are typically attached to either the pole or the sheathed ADSS cable.
While this has historically been an acceptable construction practice in the industry, as larger fiber count cables are in service (often 288 count and up), the labor and material cost of dead-ending and splicing in two places to repair minor mid-span damage can be substantial. The addition of a new span of fiber often requires a construction crew, and the splicing at each end can take a substantial amount of time. For a typical 288 count cable with only a few fibers damaged, this could result in an entire day of construction and several days of splicing. In addition to the cost, since every fiber must be spliced, arrangements must be made to render the cable out of service. Depending on the nature of the communications circuits carried by the fiber optic cable, this could result in downtime costs or penalties.
U.S. Pat. No. 8,001,686 discloses a method of taut sheath splicing of ADSS cable that includes a clamp for connecting to a first portion of the fiber optic cable and a bail for connecting the clamp to a support structure (the utility pole) and a splice closure for splicing a second portion of the fiber optic cable to one or more additional fiber optic cables, and means for connecting the splice closure to the bail (see U.S. Pat. No. 8,001,686—column 1, line 64 to column 2, line 3). One example of splicing two separate cables together is a drop to a customer (see U.S. Pat. No. 8,001,686—column 1, lines 19-22). In particular, to connect a drop fiber to a customer into an ADSS cable that does not have an existing splice point, but the disclosure of U.S. Pat. No. 8,001,686 requires the presence of a bail and support structure.
There remains a need for a method and apparatus to allow the repair or segregation of a subset of one or more fibers from a larger group within an ADSS cable, preferably also permitting the use of a mid-span device.